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Highlights Mechanistic understanding of ion transport phenomena in composite solid-state electrolytes (CSEs) for practical solid-state batteries is conducted. Percolation threshold formation of the inorganic (LPSCl) phase in the CSEs depends on elasticity of the gel polymer electrolyte (GPE) phase. Manipulating the solvation/desolvation behavior of the GPE phase facilitates ion conduction across the LPSCl-GPE interfaces.

Lithium metal batteries (LMBs) are in the spotlight as a next‐generation battery due to their high theoretical capacity. However, LMBs still suffer from inferior cycle stability owing to dendritic lithium (Li) growth during Li plating and stripping, leading to battery explosion. To solve this problem, solid electrolytes have emerged as a promising candidate by suppressing the dendritic Li growth. Despite numerous efforts, however, many challenges, such as low ionic conductivity, air stability, space charge layer, and contact loss issues, have been encountered. This review aims to provide the current challenges and new insights of solid electrolytes and then explore optimal solutions for next‐generation solid electrolytes.

Abstract Achieving satisfactory performance for a solid‐state Na‐metal battery (SSNMB) with an inorganic solid electrolyte (SE), especially under freezing temperatures, poses a challenge for stabilizing a Na‐metal anode. Herein, this challenge is addressed by utilizing a Natrium super ionic conductor (NASICON) NASICON‐type solid electrolyte, enabling the operation of a rechargeable SSNMB over a wide temperature range from −20 to 45 °C. The interfacial resistance at the Na metal/SE interface is only 0.4 Ω cm2 at 45 °C and remains below 110 Ω cm2 even at −20 °C. Remarkably, long‐term Na‐metal plating/stripping cycles lasting over 2000 h at −20 °C are achieved with minimal polarization voltages at 0.1 mA cm−2. Further analysis reveals the formation of a uniform Na3−xCaxPO4 interphase layer at the interface, which significantly contributes to the exceptional interfacial performance observed. By employing a Na3V1.5Al0.5(PO4)3 cathode, the full battery system demonstrates excellent adaptability to low temperatures, exhibiting a capacity of 80 mA h g−1 at −20 °C over 50 cycles and retaining a capacity of 108 mAh g−1 (88.5% of the capacity at 45 °C) at 0 °C over 275 cycles. This research significantly reduces the temperature threshold for SSNMB operation and paves the way toward solid‐state batteries suitable for all‐season applications.

Safe, self-standing, all-solid-state batteries with improved solid electrolytes that have adequate mechanical strength, ionic conductivity, and electrochemical stability are strongly desired. Hybrid electrolytes comprising flexible polymers and highly conductive inorganic electrolytes must be compatible with soft thin films with high ionic conductivity. Herein, we propose a new type of solid electrolyte hybrid comprising a glass–ceramic inorganic electrolyte powder (Li1+x+yAlxTi2−xSiyP3−yO12; LICGC) in a poly(ethylene)oxide (PEO)-based polymer electrolyte that prevents decreases in ionic conductivity caused by grain boundary resistance. We investigated the cross-linking processes taking place in hybrid electrolytes. We also prepared chemically cross-linked PEO/LICGC and physically cross-linked poly(norbornene)/LICGC electrolytes, and evaluated them using thermal and electrochemical analyses, respectively. All of the obtained electrolyte systems were provided with homogenous, white, flexible, and self-standing thin films. The main ionic conductive phase changed from the polymer to the inorganic electrolyte at low temperatures (close to the glass transition temperature) as the LICGC concentration increased, and the Li+ ion transport number also improved. Cyclic voltammetry using [Li metal|Ni] cells revealed that Li was reversibly deposited/dissolved in the prepared hybrid electrolytes, which are expected to be used as new Li+-conductive solid electrolyte systems.

Abstract Garnet‐type solid electrolyte is a promising candidate for the fabrication of high energy all‐solid‐state Li‐ion batteries (ASSLIBs), but its use is hampered by a large interfacial resistance. Herein, we propose a surface modification and subsequent sintering to enhance the interfacial connection between the cathode and the solid electrolyte. The ASSLIB prepared by this method delivered an initial discharge capacity of ∼66 mAh g−1 (80 °C) at a rate of 0.1 C. However, the poor contact between the cathode and electrolyte triggered the increase of the interfacial resistance, which caused severe capacity decay upon cycling. The encapsulation of LiCoO2 particles with LiBO2 using a single‐step sintering process dramatically increased the interfacial contact, resulting in a higher discharge capacity of 116 mAh g−1 with good cycling behavior. Therefore, surface modification of the cathode offers a reduction of resistance and promotes efficient Li‐ion transfer pathways across the cathode/solid‐electrolyte interface.

The polymer electrolytes are considered to be an alternative to liquid electrolytes for lithium-ion batteries because of their high thermal stability, flexibility, and wide applications. However, the polymer electrolytes have low ionic conductivity at room temperature due to the interfacial contact issue and the growing of lithium dendrites between the electrolytes/electrodes. In this study, we prepared gel polymer electrolytes (GPEs) through an in situ thermal-induced cationic ring-opening strategy, using LiFSI as an initiator. As-synthesized GPEs were characterized with a series of technologies. The as-synthesized PNDGE 1.5 presented good thermal stability (up to 150 °C), low glass transition temperature (Tg < −40 °C), high ionic conductivity (>10−4 S/cm), and good interfacial contact with the cell components and comparable anodic oxidation voltage (4.0 V). In addition, PNGDE 1.5 exhibited a discharge capacity of 131 mAh/g after 50 cycles at 0.2 C and had a 92% level of coulombic efficiency. Herein, these results can contribute to developing of new polymer electrolytes and offer the possibility of good compatibility through the in situ technique for Li-ion batteries.

In modern information technology, as integration density increases rapidly and the dimension of materials reduces to nanoscale, interfacial thermal transport (ITT) has attracted widespread attention of scientists. This review introduces the latest theoretical development in ITT through one-dimensional (1D) atomic junction model to address the thermal transport across an interface. With full consideration of the atomic structures in interfaces, people can apply the 1D atomic junction model to investigate many properties of ITT, such as interfacial (Kapitza) resistance, nonlinear interface, interfacial rectification, and phonon interference, and so on. For the ballistic ITT, both the scattering boundary method (SBM) and the non-equilibrium Green’s function (NEGF) method can be applied, which are exact since atomic details of actual interfaces are considered. For interfacial coupling case, explicit analytical expression of transmission coefficient can be obtained and it is found that the thermal conductance maximizes at certain interfacial coupling (harmonic mean of the spring constants of the two leads) and the transmission coefficient is not a monotonic decreasing function of phonon frequency. With nonlinear interaction—phonon–phonon interaction or electron–phonon interaction at interface, the NEGF method provides an efficient way to study the ITT. It is found that at weak linear interfacial coupling, the nonlinearity can improve the ITT, but it depresses the ITT in the case of strong-linear coupling. In addition, the nonlinear interfacial coupling can induce thermal rectification effect. For interfacial materials case which can be simulated by a two-junction atomic chain, phonons show interference effect, and an optimized thermal coupler can be obtained by tuning its spring constant and atomic mass.

The electrochemical stability of Li6.5La3Zr1.5Nb0.5O12 (LLZNO) and Li6.5La3Zr1.5Ta0.5O12 (LLZTO) against metallic Li was studied using direct current (DC) and electrochemical impedance spectroscopy (EIS). Dense polycrystalline LLZNO (ρ=97 %) and LLZTO (ρ=92 %) were made using sol-gel synthesis and rapid induction hot-pressing at 1100 °C and 15.8 MPa. During DC cycling tests at room temperature (±0.01 mA/cm2 for 36 cycles), LLZNO exhibited an increase in Li-LLZNO interface resistance and eventually short-circuiting while the LLZTO was stable. After DC cycling, LLZNO appeared severely discolored while the LLZTO did not change in appearance. We believe the increase in Li-LLZNO interfacial resistance and discoloration are due to reduction of Nb5+ to Nb4+. The negligible change in interfacial resistance and no color change in LLZTO suggest that Ta5+ may be more stable against reduction than Nb5+ in cubic garnet versus Li during cycling.